Intake manifolds for internal combustion engines generally comprise a manifold body formed with a plenum having an inlet and a hollow interior. A number of air passages or runners are formed in the manifold body each having an inlet at the plenum interior and an outlet connected to one of the cylinders of the engine. In many designs, a mixture of fuel and air, or air only, is directed into the interior of the plenum through a throttle valve mounted to the manifold body. The throttle valve controls the volume of air, or air-fuel mixture, entering the plenum for distribution to each of the runners.
Conventional throttle valves generally comprise a one-piece valve body having a base which is bolted to the intake manifold and a number of throughbores each mounting a throttle blade. The throttle blades are pivotally mounted within a respective throughbore by a shaft which is rotatable in response to pivoting of a throttle arm. The throttle blades are selectively movable between a fully open position and a fully closed position relative to their associated throughbores to control the flow of air and/or an air-fuel mixture therethrough and into the plenum interior of the manifold.
A number of problems inherent in the design of many throttle valves limit their effectiveness and versatility. One-piece throttle valves tend to be relatively heavy thus adding to the overall weight of the engine and reducing performance. Such valves are often difficult to service because access to the throttle blades, throttle arms, shafts and associated bearings is restricted in many of the current engine designs. If the throttle valve must be removed from the manifold to perform a service operation, a problem is presented of obtaining an effective seal with the manifold after the repairs are completed. This sealing problem can also occur if the throttle valve must be removed to accommodate different size air cleaners or supercharger bonnets, and/or different manifold bolt patterns or mounting flange configurations.
In addition to the foregoing limitations of conventional throttle valves, it has been recognized as discussed in U.S. patent application Ser. No. 08/319,294, filed Oct. 6, 1994 and entitled "Air Intake Manifold," that engine performance can suffer in the event turbulent flow is developed within the interior of the manifold. An inability to create a substantially laminar flow of air and/or an air-fuel mixture within the runners of the manifold can result in a loss of torque, decreased fuel efficiency and increased hydrocarbon emissions. Throttle valves of the type described above contribute to the creation of turbulence within the plenum interior of the manifold, and thus play a role in degrading engine performance and reducing torque output.